Environmental Science and Engineering Seminar

Hydrology, sediment or permafrost: why do high latitude rivers move so slowly?

Joel Rowland, Scientist, Los Alamos National Laboratory

ABSTRACT:

Due to climatic conditions, high latitudes have unique land surface properties and hydrology. Up to 24% of the northern hemisphere is underlain by permafrost. The presence of frozen soils strongly controls hydrological responses such as infiltration and runoff. Most high latitude rivers and streams exhibit nival hydrological regimes with snow dominated spring floods, flow limited to a fraction of the year, and ice cover during winter and spring months. Additionally, frozen soils and ground ice lead to thermally mediated erosion and creep processes. Even though three out of the 10 largest (by drainage area) rivers on earth flow across watersheds underlain by permafrost, there has, to date, been no systematic examination river erosion rates in these environments. With low sediment production rates in arctic landscapes, bank erosion in these systems is a major source of sediment to rivers and heavily influences the exchange of carbon from permafrost-dominated floodplains to rivers and oceans. Researchers have also suggested that understanding the dynamics of frozen river banks on Earth may offer insights into river development and behavior on other planets such as Mars. We measured up to four decades of bank erosion rates on over 5,000 km of high latitude rivers using satellite imagery and aerial photography. Comparing these results to our newly assembled global compilation of published erosion rates, we find that erosion rates of high latitude rivers are significantly lower than rates on lower latitude rivers. To explain this systematic difference in erosion rates, we explore the possible influences of high latitude hydrology, sediment loads, and permafrost on bank erosion rates and river migration. Based on field studies, we also explore how permafrost, ice break up, bank grain size, and hydrology influence both spatial and temporal variability in erosion rates along both a small meandering (Selawik) and a large multi-threaded (Yukon) river in Alaska.